This application is a continuation-in-part of application Serial No. 06/854,873 filed Apr. 23, 1986, now U.S. Pat. No. 4,756,037, issued July 12, 1988.
1. Field of the Invention
This invention relates to a process for dyeing successive batches of garments with a low-substantivity vat dye. The process includes the steps of rapidly impregnating each garment at or near ambient temperature with an aqueous solution of a vat dye and then shock oxidizing essentially all of the vat dye impregnated in the garment.
2. Description of the Prior Art
Indigo dye is a type of vat dye that has been known for centuries. Being a vat dye, indigo is normally insoluble in water but reducible to an amber colored water-soluble form. This soluble form, sometimes referred to as the leuco dye, is used to impregnate fibers with the dye. Subsequent oxidation insolubilizes the leuco dye and produces the final color. In the past, such oxidation has been commonly accomplished by "skying", i.e., by passing dyed yarn or fabric along an extended path through air, but this technique tends to insolubilize the dye mainly at and near the surface and has not been found satisfactory in the case of garments or heavy fabrics.
The use of indigo to dye cotton textiles in raw stock, yarn, and fabric forms is well known. See, e.g., U.S. Pat. Nos. 3,457,022 (Fields); 4,283,194 (Teague et al); and 4,342,565 (Teague et al); and Canadian Patent No. 1,098,258 (Zwier). These methods generally require considerable space and time and consume large amounts of energy due to their use of elevated dyeing or oxidation temperatures. For example, U.S. Pat. No. 3,457,022 describes a process of dyeing cotton yarn wherein indigo is first applied at a temperature of from about 65.degree. to 85.degree. C. The indigo is subsequently oxidized by skying the yarn. In order to produce the final desired color at least at and near the yarn surface, such oxidation by exposure to air is a lengthy procedure that requires several minutes for yarn lengths and on the order of hours for flat fabrics or for garments.
U.S. Pat. Nos. 4,283,194 and 4,342,565 disclose a method of dyeing relatively dry cotton yarns and fabrics wherein the indigo dye vat is maintained at a temperature of from about 55.degree. to 90.degree. C. After dyeing, the indigo dye is oxidized by skying. Chemical oxidation of the dye by use of an oxygen donor such as peroxide is mentioned but no details are given of any such chemical oxidation technique.
Canadian Patent No. 1,098,258 discloses a method for dyeing wet cotton yarn. The yarn is passed in sheet form through a wash box so as to treat the yarn with a wetting agent at about 95.degree. C. With a moisture content of about 50% based on the weight of the yarn, the yarn is cooled to about 20.degree. to 25.degree. C. and fed to at least one indigo dye bath maintained at approximately the same temperature as the cooled yarn. The yarn sheet is subsequently conveyed to an oxidizing tank maintained at about 43.degree. C. wherein the indigo dye is fixed in the yarn by a chemical oxidation agent such as sodium bichromate, sodium perborate, hydrogen peroxide, or mixtures thereof. The patent discloses that the preferred speed of the yarn sheet through the system is 50 yards per minute, or about twice the speed of dyeing yarn in rope form using the skying method of oxidizing.
The dyeing of garments or stockings on hangers or forms has also been disclosed previously. See, e.g., U.S. Pat. No. 1,873,004 (Meinig), German Patent 567,839 published 10 January 1933, and German Patent 1,920,442 published 21 January 1971. However, these references are devoid of any meaningful disclosure of the dyeing conditions, such as dye bath formulation, dye application, immersion times, oxidation of the dye, etc..
Some of the prior art referred to above as well as U.S. Pat. Nos. 810,394 (Cleff), 2,450,773 (Wehr), 3,047,354 (Santoro et al), 3,576,589 (Coon), 3,938,952 (McNeil), 4,166,717 (Fono et al), 4,310,322 (Curzons), 4,365,373 (Witte et al), 4,371,373 (Ballard), and U.K. Patent No. 732,993 (Frowein) were cited during the prosecution of applicants' parent application Ser. No. 854,873 filed Apr. 23, 1986, now U.S. Pat. No. 4,756,037, but these are merely cumulative in one respect or another or only of general interest.
There are several important advantages to dyeing garments with indigo dye as compared to making garments from indigo-dyed yarns or fabric. First, dyeing garments provides market acceptance based on rapid production rates, low capital outlays, and effective inventory control. Second, dyeing garments provides for ease of operation as the labor intensive steps of warp beam make-up and yarn quilling processes are no longer necessary. Third, dyeing garments more easily achieves a desirable color-coordinated effect in dyed garments or set of garments that contain both knit and woven patterns or that comprise jacquard patterns of different types of yarns. Fourth, this technique permits re-dyeing garments which were initially dyed incompletely, or unevenly, or otherwise to an unsatisfactory shade or color.
The advantages and essential characteristics of the garment-dyeing process of the present invention will be apparent from the following detailed description.